1. Pseudomonas pyocyanea N.C.T.C. 8203 produces a beta-lactamase that is inducible by high concentrations of benzylpenicillin or cephalosporin C. Methicillin appeared to be a relatively poor inducer, but this could be attributed in part to its ability to mask the enzyme produced. Much of the enzyme is normally cell-bound. 2. No evidence was obtained that the crude enzyme preparation consisted of more than one beta-lactamase and the preparation appeared to contain no significant amount of benzylpenicillin amidase or of an acetyl esterase. 3. The maximum rate of hydrolysis of cephalosporin C and several other derivatives of 7-aminocephalosporanic acid by the crude enzyme was more than five times that of benzylpenicillin. Methicillin, cloxacillin, 6-aminopenicillanic acid and 7-aminocephalosporanic acid were resistant to hydrolysis, and methicillin and cloxacillin were powerful competitive inhibitors of the action of the enzyme on easily hydrolysable substrates. 4. Cephalosporin C, cephalothin and cephaloridine yielded 2 equiv. of acid/mole on enzymic hydrolysis, and deacetylcephalorsporin C yielded 1 equiv./mole. Evidence was obtained that the opening of the beta-lactam ring of cephalosporin C and cephalothin is accompanied by the spontaneous expulsion of an acetoxy group and that of cephaloridine by the expulsion of pyridine. 5. A marked decrease in the minimum inhibitory concentration of benzylpenicillin and several hydrolysable derivatives of 7-aminocephalosporanic acid was observed when the size of the inoculum was decreased. This suggested that the production of a beta-lactamase contributed to the factors responsible for the very high resistance of Ps. pyocyanea to these substances. It was therefore concluded that the latter might show synergism with the enzyme inhibitors, methicillin and cloxacillin, against this organism.

Abraham & Newton (1956) showed that cephalosporin C was highly resistant to hydrolysis by purified penicillinase from BaciUu8 cereus (strain NRRL 569; see Pollock, 1959, 1960) but was a competitive inhibitor of the action of this penicillinase on benzylpenicillin. More recently, however, cephalosporin C was reported to have no significant inhibitory action on the hydrolysis of benzylpenicillin by penicillinase from a strain of Staphylococcus aureus (Abraham & Newton, 1961 a). Rolinson, Stevens, Batchelor, Wood & Chain (1960) reported that 2,6-dimethoxyphenylpenicillin was a competitive inhibitor of penicillinase from B. cereus, but not of penicillinase from Staph. aureus. These findings suggested that penicillinase from B. cereus and penicillinase from Staph. aureus differed with respect to structural features which influenced the combination of enzyme and substrate. They also drew attention to the fact that the affinity for penicillinase of a member of the cephalosporin C or penicillin family might partly determine the rate of enzymic hydrolysis of the substance in the concentration at which it was used as an antibacterial agent. The results of further experiments in this field are given here. The substances studied were N-acyl derivatives of 7-aminocephalosporanic acid which has structure (I; R = H, R' = CH3 Co00)

No abstract

The fitness effects of antibiotic resistance mutations are a major driver of resistance evolution. While the nutrient environment affects bacterial fitness, experimental studies of resistance typically measure fitness of mutants in a single environment only. We explored how the nutrient environment affected the fitness effects of rifampicin-resistant rpoB mutations in Escherichia coli under several conditions critical for the emergence and spread of resistance—the presence of primary or secondary antibiotic, or the absence of any antibiotic. Pervasive genotype-by-environment (GxE) interactions determined fitness in all experimental conditions, with rank order of fitness in the presence and absence of antibiotics being strongly dependent on the nutrient environment. GxE interactions also affected the magnitude and direction of collateral effects of secondary antibiotics, in some cases so drastically that a mutant that was highly sensitive in one nutrient environment exhibited cross-resistance to the same antibiotic in another. It is likely that the mutant-specific impact of rpoB mutations on the global transcriptome underpins the observed GxE interactions. The pervasive, mutant-specific GxE interactions highlight the importance of doing what is rarely done when studying the evolution and spread of resistance in experimental and clinical work: assessing fitness of antibiotic-resistant mutants across a range of relevant environments.

Some biological properties of cephalosporin C and of a pyridinium derivative, "cephalosporin CA (pyridine)," were examined. Staphylococci, both penicillinaseproducing and non-penicillinase-producing, and some other bacteria tested, were inhibited by 60 to 125 pg cephalosporin C/ml., and S to 20 pAg cephalosporin CA (pyridine)/ml. The ratio of the activity of the two antibiotics varied for different organisms. Resistance developed slowly on repeated subculture of penicillinaseproducing staphylococci in presence of either antibiotic. The minimum inhibitory concentration of cephalosporin CA (pyridine) upon penicillinase-producing staphylococci increased 4 to 8-fold with a 500-fold increase in inoculum size; with cephalosporin C there was a 2-fold increase. Their activity was not reduced by serum. Both substances were non-toxic. They were excreted quantitatively in the urine when given intravenously or subcutaneously to mice. After oral administration less than 5% of the dose was excreted. Cephalosporin CA (pyridine) was about 8 times more active than cephalosporin C in protecting mice from an experimental streptococcal infection, nine doses of 6.25 mg/kg affording complete protection.